In principle, in order to overcome multipath and multiple access interference in a code division multiple access (“CDMA”) spread spectrum cellular mobile communication system, especially a Time Division Duplex (“TDD”) CDMA mobile communication system, a base transceiver station (“BTS”) and a user equipment can all deploy time diversity methods to raise system performance and deploy joint detection algorithms as a basic signal detection method to suppress Multiple Access Interference (“MAI”) and Inter-Symbol Interference (“ISI”). Specifically, the BTS side can deploy smart antenna technology. In this case, by using multiple antenna units, spatial diversity gain can be obtained and with corresponding beam synthesized algorithms, receiving sensitivity can be raised (it can be understood as decreasing interference and suppressing white noise at the same time). However, at the UE side, in order to decrease cost and size, usually only one antenna is used for receiving. In this case, as multiple antenna receiving technology cannot be used, (i.e., same frequency interference and hot noise cannot be suppressed by spatial diversity), so uplink and downlink receiving gain is unmatched.
Multipath and multiple access interference can be suppressed to a maximum degree at the BTS in a CDMA spread spectrum cellular mobile communication system applying joint detection algorithms, as joint detection algorithms can estimate multipath and multiple access interference coming from all users in this cell. However, at the UE, although multipath and multiple access interference coming from the cell user can be suppressed to a maximum degree by using a joint detection algorithm, for those users at the cell edge, the joint detection algorithm cannot estimate and suppress the signal that comes from neighboring cells with the same frequency and the signal adds to the system as noise. This signal decreases system performance greatly, and the noise coefficient of the receiver limits the receiving sensitivity. In this case, if there is no appropriate signal processing method, the error rate of the receiving signal will greatly increase and the communication may even be interrupted.
Although, power control and smart antenna algorithms can suppress interference coming from neighbor cells to a maximum degree, without appropriate methods to raise UE receiving gain communication quality will also be seriously decreased and communication may even also be interrupted. For the purpose of same frequency multiplexing in a CDMA spread spectrum cellular mobile communication system, the only way to do is to decrease the working channels activated at the same time to guarantee the UE communication quality in the cells overlap area. However, this will decrease system capacity.